A dye cloud constituting a color image in subtractive color process-color photography is formed by a coupling reaction of the oxidation product of a developing agent formed during color development and a coupler. In this case, if the diffusion of the oxidation product of a developing agent is large, the dye cloud becomes large to form a mottled image (i.e., mottles), and resulting in deterioration of the graininess properties.
Various means for preventing the diffusion of the oxidation product of a developing agent for overcoming the above-described defects have been proposed.
For example, examples of a coupler blocked by a water-soluble coupler are disclosed in U.S. Pat. No. 4,310,618. Also, examples of couplers releasing diffusible couplers are described in Research Disclosure, RD No. 19633 (August, 1980) and U.S. Pat. No. 4,130,427. However, these known couplers are not totally satisfactory in the effect of controlling the gradation and the effect of improving the graininess, although they show these weak effects. Also, there is a problem of color turbidity as a fundamental defect of the releasing coupler type compound. That is, in the case of using such a compound, it is required to provide sufficient diffusibility of the dye formed by the coupling reaction of the compound to flow in a developer, but in this case, the effect of improving the graininess by the compound is reduced. This discrepancy is unavoidable.
Recently, couplers releasing an electron donor compound have been disclosed in Japanese Patent Application (OPI) No. 138,636/'82 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). However, these coupler caused various problems, such as that the coupling speed is low, which causes a problem for practical use of the compound, or the coupler residue (i.e., the structure of the other moiety (not the electron donor moiety) constituting the dye-forming moiety) has a problem, in that color images formed are poor in dark heat fading resistance property. More particularly, such cyan couplers for a red-sensitive silver halide emulsion layer have a severe problem, in that when a coupler residue showing a high coupling speed is used, the resistance to dark heat fading is poor, while when the coupler residue having good resistance to dark heat fading is used, the coupling speed is low.
Known cyan coupler residues having good dark heat fading resistance are described, for example, in U.S. Pat. Nos. 4,333,999; 4,299,914; 4,012,258, etc. However, in the case of using these known two-equivalent cyan couplers having these coupler residues, a sufficient coupling speed is not obtained.